High-strength steel bar and production method thereof

Abstract

Disclosed are a high-strength steel bar and a production method therefor. The high-strength steel bar comprises, by mass percentage, the following chemical components: C: 0.15-0.32%, Si+Mn: 0.5-1.9%, Mn+Cr+Mo+Ni: 1.1-2.1%, V: 0.02-0.8%, at least one of Nb, Ti and Al: 0.01-0.3%, and the balance of Fe and inevitable impurities; wherein Mn=(2.5-3.5)Si, and a carbon equivalent satisfies Ceq=C+Mn/6+(Cr+Mo+V)/5+(Cu+Ni)/15≤0.56%.

What is claimed is: 
     
       1. A high-strength steel bar, comprising, by mass percentage, the following chemical components: C: 0.15-0.32%, Si+Mn: 0.5-1.9%, Mn+Cr+Mo+Ni: 1.1-2.1%, V: 0.02-0.8%, at least one of Nb, Ti and Al: 0.01-0.3%, and a balance of Fe and inevitable impurities; wherein Mn=(2.5-3.5)Si, and a carbon equivalent satisfies Ceq=C+Mn/6+(Cr+Mo+V)/5+(Cu+Ni)/15≤0.56%;
 a microstructure of the high-strength steel bar comprises ferrite, pearlite, bainite and a precipitated phase; 
 the ferrite has a volume percentage of 5-35% and a size of 2-15 μm, the pearlite has a volume percentage of 30-70%, the bainite has a volume percentage of 5-35% and a size of 5-25 μm; 
 the high-strength steel bar has a yield strength≥600 MPa, a yield ratio≤0.78, an elongation after fracture≥25%, and an uniform elongation≥15%. 
 
     
     
       2. The high-strength steel bar according to  claim 1 , comprising, by mass percentage, the following chemical components: C: 0.15-0.29%, Si+Mn: 0.5-1.8%, Mn+Cr+Mo+Ni: 1.1-2.0%, V: 0.05-0.8%, at least one of Nb, Ti and Al: 0.01-0.3% and the balance of Fe and inevitable impurities; wherein Mn=(2.5-3.5)Si, and the carbon equivalent satisfies Ceq=C+Mn/6+(Cr+Mo+V)/5+(Cu+Ni)/15≤0.54%. 
     
     
       3. The high-strength steel bar according to  claim 1 , comprising, by mass percentage, the following chemical components: C: 0.15-0.32%, Si+Mn: 0.5-1.6%, Cr: 0.3-0.6%, Mn+Cr+Mo+Ni: 1.3-2.0%, V: 0.02-0.8%, at least one of Nb, Ti and Al: 0.01-0.3% and the balance of Fe and inevitable impurities; wherein Mn=(2.5-3.5)Si, and the carbon equivalent satisfies Ceq=C+Mn/6+(Cr+Mo+V)/5+(Cu+Ni)/15≤0.56%. 
     
     
       4. The high-strength steel bar according to  claim 1 , comprising, by mass percentage, the following chemical components: C: 0.15-0.32%, Si+Mn: 0.5-1.9%, Mn+Cr+Mo+Ni: 1.3-2.1%, V: 0.02-0.8%, B: 0.0008-0.002%, at least one of Nb, Ti and Al: 0.01-0.3% and the balance of Fe and inevitable impurities; wherein Mn=(2.5-3.5)Si, and the carbon equivalent satisfies Ceq=C+Mn/6+(Cr+Mo+V)/5+(Cu+Ni)/15≤0.56%. 
     
     
       5. The high-strength steel bar according to  claim 4 , comprising, by mass percentage, the following chemical components: C: 0.15-0.32%, Si+Mn: 0.5-1.9%, Mn+Cr+Mo+Ni: 1.1-2.1%, V: 0.02-0.8%, B: 0.0008-0.002%, at least one of Nb and Al: 0.01-0.3%, Ti: 0.01-0.1% and the balance of Fe and inevitable impurities; wherein Ti/N≥1.5, Mn=(2.5-3.5)Si, and the carbon equivalent satisfies Ceq=C+Mn/6+(Cr+Mo+V)/5+(Cu+Ni)/15≤0.56%. 
     
     
       6. The high-strength steel bar according to  claim 1 , wherein the cross-sectional diameter of the high-strength steel bar is 14-18 mm, the content of C is 0.15-0.3% by mass percentage, and the carbon equivalent Ceq is 0.40-0.52%; or
 the cross-sectional diameter of the high-strength steel bar is 20-22 mm, the content of C is 0.15-0.3% by mass percentage, and the carbon equivalent Ceq is 0.52-0.54%. 
 
     
     
       7. The high-strength steel bar according to  claim 1 , wherein the precipitated phase has a size≤100 nm and a volume content≥2*10 5 /mm 3 . 
     
     
       8. The high-strength steel bar according to  claim 1 , wherein the ferrite has a volume percentage of 8-30% and a size of 3-12 μm, the pearlite has a volume percentage of 35-65%, the bainite has a volume percentage of 8-35% and a size of 6-22 μm, and the precipitated phase has a size≤80 nm and a volume content≥5*10 5 /mm 3 . 
     
     
       9. The high-strength steel bar according to  claim 1 , wherein the ferrite has a volume percentage of 10-25% and a size of 4-10 μm, the pearlite has a volume percentage of 40-60%, the bainite has a volume percentage of 15-35% and a size of 8-20 μm, and the precipitated phase has a size≤60 nm and a volume content≥8*10 5 /mm 3 . 
     
     
       10. The high-strength steel bar according to  claim 1 , wherein the high-strength steel bar has no obvious yield platform in a stress-strain curve of a tensile test and an impact toughness≥160 J under a test condition of −20° C. 
     
     
       11. The high-strength steel bar according to  claim 1 , wherein the high-strength steel bar comprises a base material and a flash butt welding junction, and the high-strength steel bar has a fracture point formed at the base material in a tensile test. 
     
     
       12. A production method of the high-strength steel bar according to  claim 1 , wherein the production method comprises the following steps:
 a smelting process: performing smelting on molten steel in an electric furnace or a converter; 
 a continuous casting process: preparing the molten steel into a continuous casting billet through a continuous casting machine, wherein the superheat degree of the molten steel during continuous casting is 15-30° C.; 
 a temperature-controlled rolling process: rolling the continuous casting billet into the steel bar in a heating furnace at a heating temperature of 1200-1250° C. for 60-120 min, wherein the initial rolling temperature is 1000-1150° C., and the finish rolling temperature is 850-950° C.; 
 a temperature-controlled cooling process: cooling the steel bar at a temperature of 800-920° C. on a cooling bed. 
 
     
     
       13. The production method of the high-strength steel bar according to  claim 12 , wherein the smelting process comprises an argon blowing refining process, and according to the argon blowing refining process, argon bottom blowing at a pressure of 0.4-0.6 MPa is used to perform soft stirring on the refined molten steel for not less than 5 min. 
     
     
       14. The production method of the high-strength steel bar according to  claim 12 , wherein the molten steel is subjected to electromagnetic stirring during continuous casting with an electromagnetic stirring parameter of 300 A/4 Hz and a final electromagnetic stirring parameter of 480 A/10 Hz. 
     
     
       15. The production method of the high-strength steel bar according to  claim 12 , wherein in the continuous casting process, the straightening temperature of the continuous casting billet≥850° C. 
     
     
       16. The production method of the high-strength steel bar according to  claim 12 , wherein in the temperature-controlled cooling process, the steel bar at a temperature of 820-900° C. is cooled on the cooling bed at a cooling rate of 2-5° C./s.